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2. 1-2 Access networks and physical media Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated?

3. 1-3 Residential access: point to point access Dialup via modem ▫ up to 56Kbps direct access to router (often less) ▫ Can’t surf and phone at same time: can’t be “always on”  ADSL: asymmetric digital subscriber line  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  ADSL2+ 24Mbps

4. 1-4 Residential access: cable modems HFC: hybrid fiber coax ▫ asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router ▫ homes share access to router deployment: available via cable TV companies

5. 1-5 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

6. 1-6 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes

7. 1-7 Cable Network Architecture: Overview home cable headend cable distribution network server(s)

8. 1-8 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)

9. 1-9 Cable Network Architecture: Overview home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL 1234 56789 FDM:

10. 1-10 Company access: local area networks company/univ local area network (LAN) connects end system to edge router Ethernet: ▫ shared or dedicated link connects end system and router ▫ 10 Mbs, 100Mbps, Gigabit Ethernet

11. 1-11 Wireless access networks shared wireless access network connects end system to router ▫ via base station aka “access point” wireless LANs: ▫ 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access ▫ provided by telco operator ▫ 3G ~ 384 kbps  Will it happen?? ▫ GPRS ▫ WiMAX base station mobile hosts router

12. 1-12 Home networks Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet

13. 1-13 Physical Media Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: ▫ signals propagate in solid media: copper, fiber, coax unguided media: ▫ signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires ▫ Category 3: traditional phone wires, 10 Mbps Ethernet ▫ Category 5: 100Mbps Ethernet

14. 1-14 Physical Media: coax, fiber Coaxial cable: two concentric copper conductors bidirectional baseband: ▫ single channel on cable ▫ legacy Ethernet broadband: ▫ multiple channels on cable ▫ HFC Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation:  high-speed point-to-point transmission (e.g., 10’s- 100’s Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise

15. 1-15 Physical media: radio signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: ▫ reflection ▫ obstruction by objects ▫ interference Radio link types:  terrestrial microwave  e.g. up to 45 Mbps channels  LAN (e.g., Wifi)  11Mbps, 54 Mbps  wide-area (e.g., cellular)  e.g. 3G: hundreds of kbps  satellite  up to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude

16. Teleports A telecommunications port—or, more commonly, teleport—is a satellite ground station with multiple parabolic antennas (i.e., an antenna farm) that functions as a hub connecting a satellite or geocentric orbital network with a terrestrial telecommunications network. Teleports may provide various broadcasting services among other telecommunications functions, such as uploading computer programs or issuing commands over an uplink to a satellite. 16

17. Teleports 17 Balambu Earth Station: Nepal Telecom=>Teleport

18. Satellites Geostationary Satellites Medium-Earth Orbit Satellites Low-Earth Orbit Satellites 18

19. Geostationary Satellites At altitude approx. 36000Km above equatorial plane, satellite rotation period is 24hrs. Satellite is stationary with respect to Earth. With current technology, it is unwise to have geostationary satellites spaced much closer than 2 degrees in the 360- degree equatorial plane, to avoid interference. With a spacing of 2 degrees, there can only be 360/2 = 180 of these satellites in the sky at once. However, each transponder can use multiple frequencies and polarizations to increase the available bandwidth. 19

20. Medium-Earth Orbit Satellites At much lower altitudes, we find the MEO (Medium-Earth Orbit) satellites. As viewed from the earth, these drift slowly in longitude, taking something like 6 hours to circle the earth. Accordingly, they must be tracked as they move through the sky. Because they are lower than the GEOs. GPS (Global Positioning System) satellites orbiting at about 18,000 km are examples of MEO satellites. 20

21. Low-Earth Orbit Satellites Moving down in altitude, we come to the LEO (Low-Earth Orbit) satellites. Due to their rapid motion, large numbers of them are needed for a complete system. On the other hand, because the satellites are so close to the earth, the ground stations do not need much power, and the round-trip delay is only a few milliseconds. 21

22. Satellite 22

23. Terrestrial Radio Links Radio channels carry signals in the electromagnetic spectrum. They are an attractive media because require no physical "wire“ to be installed, can penetrate walls, provide connectivity to a mobile user, and can potentially carry a signal for long distances. The characteristics of a radio channel depend significantly on the propagation environment and the distance over which a signal is to be carried. 23

24. Terrestrial Radio Links those that operate as local area networks (typically spanning 10's to a few hundred meters) e.g. WLAN and wide-area radio channels that are used for mobile data services (typically operating within a metropolitan region) e.g. WAP, 3G etc 24

25. Satellite frequency band L-bank (1-2GHz) C-Bank (4-8GHz) KU-Band (12-18GHz) KA-Band (26.5-40GHz) 25

26. Satellite frequency band L-bank (1-2GHz) ▫ Being a relatively low frequency, L-band is easier to process, requiring less sophisticated and less expensive RF equipment. ▫ L-Band is also used for low earth orbit satellites, military satellites, and terrestrial wireless connections like GSM mobile phones. It is also used as an intermediate frequency for satellite TV where the Ku or Ka band signals are down-converted to L-Band at the antenna C-Bank (4-8GHz) ▫ Satellite C-band usually transmits around 6 GHz and receives around 4 GHz. It uses large (2.4- 3.7 meter) antennas ▫ C-band is typically used by large ships that traverse the oceans on a regular basis and require uninterrupted, dedicated, always on connectivity as they move from region to region. ▫ C-band is also used for terrestrial microwave links 26

27. Satellite frequency band KU-Band (12-18GHz) ▫ Ku-Band is most commonly used for satellite TV and is used for most VSAT systems. ▫ There is much more bandwidth available in Ku -Band and it is therefore less expensive that C or L-band. ▫ Ku band coverage is generally by regional spot beams, covering major land areas with TV reception ▫ VSAT Antenna sizes typically range from the standard 1 meter, to 1.5 meters & as low as 60cm for spread spectrum operation KA-Band (26.5-40GHz) ▫ is an extremely high frequency requiring great pointing accuracy and sophisticated RF equipment. ▫ It is commonly used for high definition satellite TV. It is also used today for terrestrial VSAT services 27

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29. Internet service provider An Internet service provider (ISP) is an organization that provides access to the Internet. Access ISPs directly connect clients to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs are a kind of colocation center that leases server space to smaller businesses and other people. Transit ISPs provide large amounts of bandwidth for connecting hosting ISPs to access ISPs 29

30. ISPs Tier1 Tier2 and Tier3 ISPS 30

31. 1-31 Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable and Wireless), national/international coverage ▫ treat each other as equals Tier 1 ISP Tier-1 providers interconnect (peer) privately NAP Tier-1 providers also interconnect at public network access points (NAPs)

32. 1-32 Tier-1 ISP: e.g., Sprint Sprint US backbone network Seattle Atlanta Chicago Roachdale Stockton San Jose Anaheim Fort Worth Orlando Kansas City Cheyenne New York Pennsauken Relay Wash. DC Tacoma DS3 (45 Mbps) OC3 (155 Mbps) OC12 (622 Mbps) OC48 (2.4 Gbps) … to/from customers peering to/from backbone …. … … … POP: point-of-presence

33. 1-33 Internet structure: network of networks “Tier-2” ISPs: smaller (often regional) ISPs ▫ Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other, interconnect at NAP

34. 1-34 Internet structure: network of networks “Tier-3” ISPs and local ISPs ▫ last hop (“access”) network (closest to end systems) Tier 1 ISP NAP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

35. 1-35 Internet structure: network of networks a packet passes through many networks! Tier 1 ISP NAP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

36. Delays As a packet travels from one node to the subsequent node along the path, the packet suffers from several different types of delays at each node along the path. The most important of these delays are the ▫ Nodal processing delay /Processing Delay ▫ Queuing delay ▫ Transmission delay and ▫ Propagation delay 36

37. Delays Nodal processing delay /Processing Delay ▫ The time required to examine the packet's header and determine where to direct the packet is part of the processing delay. ▫ The processing delay can also include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet's bits from the upstream router to router Queuing delay ▫ After this nodal processing, the router directs the packet to the queue that precedes the link to router B. ▫ At the queue, the packet experiences a queuing delay as it waits to be transmitted onto the link. ▫ The queuing delay of a specific packet will depend on the number of other, earlier-arriving packets that are queued and waiting for transmission across the link; the delay of a given packet can vary significantly from packet to packet. ▫ If the queue is empty and no other packet is currently being transmitted, then our packet's queuing delay is zero 37

38. Delays Transmission Delay ▫ The amount of time required to transmit all of the packet's bits into the link. Propagation Delay ▫ The time required to send packet from one router to another router. The bit propagates at the propagation speed of the link. ▫ The propagation speed depends on the physical medium of the link and the distance from source to destination. Total Delay ▫ Total Delay d total = d proc + d queue + d trans + d prop If there is N node and all the delays are same then the total delay is ▫ Total Delay d total = N (d proc + d queue + d trans + d prop) 38